T-Cell-Positive, B-Cell-Negative Flow Cytometry Crossmatch: Frequency, HLA Locus Specificity, and Mechanisms Among 3073 Clinical Flow Cytometry Crossmatch Tests.

OBJECTIVES: A T-cell-positive and B-cell-negative flow cytometry crossmatch result remains a conundrum since HLA class I antigens are expressed on both T and B cells. We investigated the frequency, donor HLA specificity of the antibodies, and mechanisms for these crossmatch results. MATERIALS AND METHODS: We analyzed 3073 clinical flow cytometry crossmatch tests performed in an American Society of Histocompatibility and Immunogeneticsaccredited histocompatibility laboratory. The sera associated with the T-cell positive and B-cell negative flow cytometry crossmatches were also tested for donor HLA immunoglobulin G antibodies using LABScreen single antigen assays. RESULTS: Among the 3073 test results, 1963 were T-cell negative and B-cell negative, 811 were T-cell negative and B-cell positive, 274 were T-cell positive and B-cell positive, and 25 were T-cell positive and B-cell negative. The LABScreen single antigen assay detected HLA class I immunoglobulin G donor-specific antibodies in 23 of 25 sera associated with a T-cell positive and B-cell negative flow cytometry crossmatch result, and donorspecific antibodies directed at not only HLA-Cw but also at HLA-A or HLA-B were observed. In addition, we identified that the B-cell channel shift threshold used to classify a B-cell flow cytometry crossmatch was a potential contributor to a T-cell-positive and B-cellnegative flow cytometry crossmatch result. CONCLUSIONS: Our analysis of 3073 flow cytometry crossmatches, in addition to demonstrating that HLA antibodies directed at the HLA-A, -B, or -Cw locus were associated with a T-cell-positive and B-cell-negative result, identified mechanisms for the surprising T-cell-positive and B-cell-negative flow cytometry crossmatch result.

Successful A2 to B Deceased Donor Kidney Transplant after Desensitization for High-Strength Non-HLA Antibody Made Possible by Utilizing a Hepatitis C Positive Donor.

Desensitization using plasma exchange can remove harmful antibodies prior to transplantation and mitigate risks for hyperacute and severe early acute antibody-mediated rejection. Traditionally, the use of plasma exchange requires a living donor so that the timing of treatments relative to transplant can be planned. Non-HLA antibody is increasingly recognized as capable of causing antibody-mediated renal allograft rejection and has been associated with decreased graft longevity. Our patient had high-strength non-HLA antibody deemed prohibitive to transplantation without desensitization, but no living donors. As the patient was eligible to receive an A2 ABO blood group organ and was willing to accept a hepatitis C positive donor kidney, this afforded a high probability of receiving an offer within a short enough time frame to attempt empiric desensitization in anticipation of a deceased donor transplant. Fifteen plasma exchange treatments were performed before the patient received an organ offer, and the patient was successfully transplanted. Hepatitis C infection was treated posttransplant. No episodes of rejection were observed. At one-year posttransplant, the patient maintains good graft function. In this case, willingness to consider nontraditional donor organs enabled us to mimic living donor desensitization using a deceased donor.

Acute Rejection, Kidney Allograft Function, and Graft Survival in Patients with Circulating Pre-Transplant IgG Antibodies Directed Against Donor HLA-A, -B, or -C Locus Determined Antigens.

The relationship between circulating pre-transplant immunoglobulin G (IgG) antibodies to donor human leukocyte antigen (HLA) -C locus determined antigens alone and acute rejection, kidney allograft function, and graft survival is not fully defined. Also, the impact of circulating pre-transplant IgG antibodies to donor HLA-C locus antigens alone on these outcomes has not been compared with the impact of circulating pre-transplant IgG antibodies to donor HLA-A or -B locus antigens. We conducted a retrospective review of records of 1252 kidney allograft recipients transplanted at our center between January 2010 and January 2016 to identify patients with circulating pre-transplant IgG antibodies directed at kidney donor HLA-A, -B, or -C locus determined antigens. Antibodies were detected and reported using the LABScreen Single Antigen Bead assay with microbeads coated with single HLA class I antigens. Pre-transplant and post-transplant data were collected and the graft outcomes of 16 kidney graft recipients with antibodies to HLA-C locus antigens were compared to the outcomes in 56 recipients with antibodies to HLA-A or -B locus determined antigens. The one-year acute rejection rate was 6% in those with donor-specific antibodies (DSA) to HLA-C locus antigens and 20% in those with DSA to HLA-A or -B locus antigens. The graft survival rate was 100% in those with DSA to HLA-C locus antigens and 95% in those with DSA to HLA-A or -B locus antigens. None of the numerical differences were statistically significant (p>0.05). The presence of circulating pre-transplant IgG antibodies directed at kidney donor HLA-C locus antigens alone may not be associated with an increased risk of acute rejection or a decreased graft survival rate. Our observations support the concept that circulating pre-transplant IgG antibodies directed at kidney donor HLA-C locus antigens alone do not negatively impact kidney allograft outcomes and that the mean fluorescence intensities of the antibodies directed at HLA-C locus alone should not be used to list unacceptable HLA-C locus antigens for kidney allocation. A study with a larger cohort is needed to investigate our hypothesis.

Characteristics of Circulating Donor Human Leukocyte Antigen-specific Immunoglobulin G Antibodies Predictive of Acute Antibody-mediated Rejection and Kidney Allograft Failure.

BACKGROUND: Characteristics of pretransplant antibodies directed at donor human leukocyte antigen (HLA) donor-specific antibodies (DSA) associated with adverse outcomes in kidney transplant recipients are being elucidated but uncertainties exist. METHODS: We prospectively screened pretransplant sera from 543 kidney recipients using single antigen bead assays and identified 154 patients with and 389 without DSA. We investigated the association of DSA features to acute rejection and graft failure. RESULTS: One-year acute rejection incidence was higher in DSA-positive group (P < 0.001), primarily due to antibody-mediated rejection (AMR, 13% vs. 1.8%, P < 0.001) and not T cell-mediated rejection (ACR, 5% vs.6%, P = 0.65). The sum of mean fluorescence intensity of DSA (DSA MFI-Sum) of 6,000 or higher (OR, 18; 95% CI, 7.0-47; P < 0.001) and the presence of DSA against both HLA class I and II (OR, 39; 95% CI, 14-106; P < 0.0001) predicted 1-year AMR, independent of other covariates. Calculated panel reactive antibody and a positive flow cytometry cross-match result were associated with AMR by bivariate analysis but neither was an independent predictor in a multivariable regression analysis that included DSA-MFI-Sum or HLA DSA class. In multivariable Cox proportional hazards models, the covariate-adjusted hazard ratio for graft failure was 2.03 (95%CI, 1.05-3.92; P = 0.04) for DSA MFI-Sum of 6,000 or higher and 2.23 (95% CI, 1.04-4.80; P = 0.04) for class I and II DSA. Prediction of graft failure was not independent of AMR. CONCLUSION: Our study suggests that DSA MFI-Sum and HLA class of DSA are characteristics predictive of AMR and graft failure. The elevated risk of graft failure in those with the identified features of DSA is attributable to increased risk of AMR.

Effect of high-dose intravenous immunoglobulin on anti-HLA antibodies in sensitized kidney transplant candidates.

Limited data exist on the effect of intravenous immunoglobulin (IVIg) on anti-HLA antibodies as determined by solid-phase assays. We reviewed our experience treating sensitized wait-listed kidney transplant recipients with IVIg as a method for desensitization and report our results utilizing Luminex single antigen (LSA) bead assay to quantify antibody reactivity (MFI). Fifteen patients with a cPRA > 40% received 2 g/kg IVIg per month for four months or until transplanted. LSA testing was performed before and after IVIg. Median MFI for anti-class I antibodies fell in 11 (73%) and increased in 4 (27%) patients after IVIg. Similar significant changes in MFI for anti-class II antibodies were observed in 10 patients (66%). Administration of IVIg was associated with a modest decrease in reactivity to both class I and II HLA antigens (median MFI change 493 and 1110, respectively; p < 0.0001) but did not significantly alter mean cPRA (85% before IVIg vs. 80% after IVIg; p = 0.1). Our data suggest a smaller effect of IVIg on HLA antibody reactivity than previously described, leading us to question how best to measure the efficacy of a desensitization protocol in current practice.

Changes in IgG subclasses of donor specific anti-HLA antibodies following bortezomib-based therapy for antibody mediated rejection.

The predominant anti-HLA IgG subclass during antibody mediated rejection episodes is IgG1. Class I DSA IgG subclasses respond to single cycle of bortezomib-based therapy more frequently as compared to Class II DSA IgG subclasses. High titer Class II DSA IgG subclasses are less likely to respond to single cycle bortezomib-based therapy. Future studies are needed to determine if the response to bortezomib-based therapy is dependent on the type of DSA and/or the strength of the DSA at the time of antibody mediated rejection episode.

Addition of plasmapheresis decreases the incidence of acute antibody-mediated rejection in sensitized patients with strong donor-specific antibodies.

BACKGROUND AND OBJECTIVES: The objective of this study was to investigate the effects of desensitization protocols using intravenous Ig with or without plasmapheresis in patients with donor-specific anti-HLA antibodies on prevention of antibody-mediated rejection and downregulation of donor-specific antibodies. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: Thirty-five complement-dependent cytotoxicity T cell cross-match-negative but complement-dependent cytotoxicity B cell and/or flow cytometry cross-match-positive kidney transplant recipients were treated with high-dosage intravenous Ig plus Thymoglobulin induction treatment. Donor-specific antibody strength was stratified as strong, medium, or weak by Luminex flow beads. Group 1 patients had weak/moderate and group 2 strong donor-specific antibodies RESULTS: Whereas no group 1 patients had acute rejection, 66% of group 2 had acute rejection (44% antibody-mediated rejection, 22% cellular rejection). The protocol was then changed to the addition of peritransplantation plasmapheresis to patients with strong donor-specific antibodies (group 3). This change resulted in a dramatic decrease in the acute rejection rate to 7%. During a median 18 mo of follow-up, patient survival was 100, 100, and 93% and graft survival was 100, 78, and 86% in groups 1, 2, and 3, respectively. During follow-up, 17 (52%) patients lost donor-specific antibodies completely, and 10 (30%) lost some of donor-specific antibodies and/or decreased the strength of existing donor-specific antibodies. CONCLUSIONS: These results indicated that in patients with strong donor-specific antibodies, the addition of plasmapheresis to high-dosage intravenous Ig decreases the incidence of acute rejection. The majority of the patients, whether they received intravenous Ig alone or with plasmapheresis, lost their donor-specific antibodies during follow-up.

Transplant glomerulopathy may occur in the absence of donor-specific antibody and C4d staining.

BACKGROUND AND OBJECTIVES: Transplant glomerulopathy (TGP) has been proposed to be a component of chronic antibody-mediated rejection (AMR). We have studied 36 patients with TGP and 51 patients with chronic allograft nephropathy (CAN) but without TGP for C4d staining and donor-specific anti-HLA antibodies (DSA) to investigate the alloantibody-mediated mechanisms. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: Allograft biopsies were stained with C4d staining and DSAs were studied by Luminex Flow Beads. Allograft biopsies were done at a mean of 5.3 +/- 5.0 and 5.6 +/- 4.6 yr after transplantation in patients with CAN and TGP, respectively. RESULTS: The mean creatinine level at the time of the biopsy was 2.7 +/- 1.2 mg/dl in each group. Proteinuria of >1.0 g/d was more common in patients with TGP (61 versus 25%; P = 0.002). Whereas three patients with TGP had a history of acute AMR, none of the patients with CAN had. Mean chronicity score of the biopsies were 1.7 +/- 0.7 in patients with CAN and 1.9 +/- 0.8 in patients with TGP. Biopsies from only two (4%) patients with CAN and four (11%) patients with TGP had diffuse C4d positivity. DSA were found in 36% of TGP and 33% of CAN patients. CONCLUSIONS: These results suggest that a substantial number of patients with TGP did not have positive C4d staining or DSA, indicating that a non-alloantibody-mediated process may be involved in the development of TGP in some patients.